The present invention relates to an electrophotographic recording material comprising an electrically conductive support and a photoconductive layer which comprises a photoconductor, a particular cyanine dye serving as the sensitizing dye, a binder, and customary additives.
In electrophotographic reproduction processes, it is known to use photoconductors that are radiation-sensitive up to the short-wave visible portion of the spectrum and that display a radiation-sensitivity in the visible portion of the spectrum which can be extended by adding one or more sensitizing dyes capable of transmitting the energy of longer-wavelength light to the photoconductor. Such sensitizing dyes include dyes of a wide variety of chemical types.
German Auslegeschrift No. 2,526,720 (corresponding to U.S. Pat. No. 4,063,948) discloses an electrophotographic recording material for an electrophotographic reproduction process, in which the photoconductive layer contains a cyanine dye that sensitizes in the blue spectral region. With a sensitization of this type it is, however, impossible to utilize the energy of light sources emitting light with a high red fraction such as, for example, incandescent lamps.
From German Offenlegungsschrift No. 1,447,907 (corresponding to U.S. Pat. No. 3,458,310), it is known to sensitize photoconductor layers up to the visible red. For this purpose, dye mixtures of, for example, Acridine Yellow, Acridine Orange, Rhodamine and and Brilliant Green are used, which are added either together in one layer or separately in different layers, as disclosed in German Offenlegungsschrift No. 2,353,639 (corresponding to U.S. Pat. No. 3,992,205) and in which the actions of the individual dyes either add up or a different sensitization occurs, as disclosed in German Offenlegungsschrift No. 2,817,428 (corresponding to U.S. Pat. No. 4,252,880).
Panchromatic sensitizations of this kind offer advantages, in that light sources having a high red fraction, which are used in reproduction techniques, are better utilized. In practice, this results in shorter exposure times and, as a consequence, time and energy are saved. Due to the improved sensitivities, it is also possible to reduce the amount of photoconductor in the photoconductive layer.
It is, however, a disadvantage of panchromatic sensitizations that the sensitized material cannot be processed in bright safelights which are physiologically favorable.
Many of the dyes which strongly sensitize in the red spectral region, preferably the dyes from the class of triphenylmethane dyes, produce a very broad sensitization, but the peak of this sensitization is generally not above about 650 nm. As a result, light sources emitting in the longer-wavelength region cannot be fully utilized, and it is also impossible to process the material in bright safelights without spoiling it.
According to U.S. Pat. No. 4,386,146, photoconductor layers for photosensitive papers containing titanium dioxide as the photoconductor are sensitized with widely differing cyanine dyes. The materials are intended for use in color electrophotography. From the fact that the cyanine dyes sensitize titanium dioxide it cannot be concluded, however, that they are also suitable for use in photoconductors, the electrophotographic behavior of which is different from that of titanium dioxide. The known cyanine dyes have a sensitizing action which covers a wide range of wavelengths. This is, however, a disadvantage if the material is to be processed and controlled in visible light in the darkroom.